Means for detection and control of liquid level in a vessel

ABSTRACT

A vessel has a source and detectors of radiation emplaced within containers extended through its walls so the level of a fluid within the vessel will be detected by interference of the fluid with the reception of the radiation by the detectors.

45] Apr. 4, 1972 ...250/43.S FL .....250/43.5 FL ....250/43.5 FL

1/1966 Preiiwitz.................

m G 3 5 9 1 2 l 5 no 2 6 2 2,981,841 4/1961 Wheeler......... 3,230,363

[54] MEANS FOR DETECTION AND CONTROL OF LIQUID LEVEL IN A VESSEL [72]inventors:

g- John FOREIGN PATENTS OR APPLiCATiONS S8, 8-

1,094,475 12/1960 Germany............................

[73] Assignee: Combustion Engineering, Inc., New York,

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UNITED STATES PATENTS PATENTEDAPR 4 I972 3,654,458

/N VE N TORS.

HILL 5. BURRUS JOHN B. R0550 ATTORNEY MEANS FOR DETECTION AND CONTROL OFLIQUID LEVEL IN A VESSEL BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to mounting a radiation sourceand detector within a container in a closed vessel so the level of afluid within the vessel can be detected for manifestation and/orcontrol. More particularly, the invention relates to a structure andarrangement whereby a source of radiation and one or more detectors ofthe radiation can be inserted into a thin-walled container, in turnmounted in a thick-walled vessel, for detection and control of the fluidlevel within the vessel. The source and detector assemblies can beremoved from their containers for repair, service and replacementwithout opening the vessel.

2. Description of the Prior Art The oil industry is on the threshold ofthe initial separation, at subsea locations, of subsea oil wellproduction. Until now, marine oil well production has been brought tothe surface for field processing prior to transportation by pipeline todistant points for final preparation for its use. As subsea wells areproduced at depths below 150 feet, conducting the oil well production tothe surface creates a large number of problems not present at theshallower depths; for example, pressure reductions and heat loss in wellfluids may cause hydrate formation in flow lines. An analysis of theseenvironmental problems of subsea production and field processing wasmade in US. Pat. No. 3,550,385.

Consequently, current deep-water production technology requires that atleast the initial separation process (i.e., of the liquid and vaporphases) of wells produced from depths below approximately 150 feet beaccomplished in vessels situated at or near the marine wellhead or onsubsurface producing platforms. These vessels must be able to operate atdepths of at least 1,000 feet. One of the requirements of this equipmentis that the levels of the fluids produced through the vessels be sensedand manifested for control action to be taken which will affect thelevels.

There is obvious difficulty in using most of the level detection andcontrol devices developed for land-based production equipment in subseainstallations. Many of them use gas as an energy source, and operationof gas-powered devices designed for surface use at the subsea depthsunder consideration requires extensive modification. However,radiation-type level controls can be successfully used under suchconditions without extensive modification.

Level controls using radioactive energy have long been known in the art.Their use is disclosed in at least US. Pat. Nos. 2,565,963 issued Aug.28, 1951, and 2,734,136 issued Feb. 7, 1956. Illustrative andwell-explained commercial applications are disclosed in the producecatalog of IN-VAL- CO, a division of Combustion Engineering, Inc.,Tulsa, Oklahoma, at pages 143, 144, 201, and 202.

SUMMARY OF THE INVENTION A principal object of the invention is toprovide an improved mounting system for a radiation level detectorwithin a thick-walled vessel in which liquid has a level to be detectedand manifested and/or controlled.

Another object is to provide an improved manner of installation andremoval of the radioactive source and detector elements within a vesselwithout opening the vessel.

Another object is to provide increased protection of the source frommarine growth and the chemical properties of fluids outside the vessel.

Another object is to more efficiently heat exchange the detectorelements with fluids outside the vessel to prevent their overheatingfrom the fluids within the vessel.

The invention contemplates at least two containers extended through thetank walls of a vessel containing fluid whose level is to be detected.The containers have a source of radiation mounted in one of them and adetector element mounted in the other. The fluid rises until itpartially shields one or more of the detectors from the radiation of thesource. The level is thereby sensed and manifested by a responsivecircuit including the detectors.

The radiation source and detector elements within the containersextended through the walls of the vessel are not in communication withthe interior of the vessel except through the radiation of the source.Therefore, the source and the detectors can be inserted in and removedfrom their containers without opening the vessel.

The invention also contemplates the source container being filled with asubstance which will obviate contact between the radioactive source anddeleterious fluids external the container while resisting the largeworking pressures usually present within the vessel. I

Also, conduits in the detector container communicating with the fluidsexternal the vessel provide a path for convection circulation of theexternal fluids, the heated fluids of the container generating thecirculation.

Other objects, advantages and features of this invention will becomeapparent to one skilled in the art upon consideration of the writtenspecification, appended claims, and attached drawings, wherein;

FIG. 1 is a cross-sectioned elevation of a vessel and level controlembodying the invention, together with the electrical system forindicating, recording, and controlling the liquid level in the sealedcontainer;

FIG. 2 is an elevation view of the radiation source assembly as itappears when not in place in its container in a vessel; and

FIG. 3 is an elevation view of the detector/electronics assembly as itappears when not in place in its container in vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENT The Operating Situation The mostobvious environment for the present invention is now beneath the surfaceof a body of water. The most practical use for the invention is indetection and manifestation of liquid levels within tanks or pressurevessels into which oil wells are produced.

Heretofore, subsea oil wells have been produced into vessels mounted ator above the marine surface. Now that wells in water feet deep, andforeseeably much deeper, are to be produced, the vessels initiallyreceiving the production must be located below the surface. Such vesselsmay be mounted subsurface on a platform deck or on the marine bottom atthe wellhead.

Vessels initially receiving the well production must be thickwalled tohold the high pressure reservoir fluids produced into them. Thethicknesses required are too great to be penetrated with a standardintensity radioactive source material used for sensing the level ofliquids within a container. The disadvantages of using source materialin a level control device hot enough to penetrate a 4-to6 inch steelwall of such a vessel are apparent.

The Flow Pattern The drawing of FIG. I discloses how the inventionsolves the problem of constructively positioning a source and detectorof radiation within a vessel for detection of the level of liquid withinthe vessel. The vessel 1 is cylindrical, the view being a cross-sectionin elevation.

The vessel wall 2 is shown as being relatively thick, too thick for aradioactive source of acceptably low intensity to be used to penetratethe wall and sense the level. Thus containers 3, 4 of a suitablethin-walled material penetrate thick wall 2 and receive the radiationsource assembly 5 and detector elements 6, 7, 8 within the vessel. It isexpected that operators will deal routinely with pressures of 2,000 psiin vessel 1, requiring vessel wall thicknesses of 4 to 6 inches,depending on the vessel diameter. Furthermore, improved fabricationmethods may allow them greater wall thickness and thus larger diametervessels. However, in the arrangement disclosed, wall thicknesses of onlyc. 0.6 inches in containers 3, 4 need be provided for containerdiameters of 3 to 4 inches to withstand the pressure in the vessel.Containers 3, 4 are disclosed securely welded at intersections 9 withthe vessel shell to prevent all leakage of vessel contents to theatmosphere (i.e., the sea in the proposed subsea installation).

Produced well fluids enter the vessel 1 through conduit 10 ordinarily ata pressure significantly higher than the working pressure of the vessel.Choke 11 is shown to illustrate a manner in which the pressure of theconduit 10 fluids, and therefore the pressure within vessel 1 isregulated. The fluids then pass through remote-actuated valve 12 at apredetermined rate. Processed fluids exit the vessel through conduit 13as controlled by remote-actuated valve 14.

Numeral 15 illustrates the interfacial zone, herein noted as the liquidlevel to be controlled, between fluids in the vapor phase and fluids inthe liquid phase. Optimum process conditions are achieved when thislevel is fixed and held at some predetermined height in the vessel.Detector 7 is shown in position to maintain this level by generatingmore or less current through electronic network 16 as the level falls orrises from the desired position at 15. Detector 7 is referred to as thenormal level controller.

Detectors 6, 8 are high level and low level controls, respectively. Ifthe level becomes too high or too low in the vessel, the decrease orincrease in current to network 16 can signal an alarm and conduct asupervisory function, and valves 12, 14 will isolate the intake or exitfunctions as required. Valves 12, 14 are, of course, well-knownthrottling type valves, and minor fluctuations in the level 15 areadjusted by the throttling open or closed of valve 12 or valve 14, asrequired. Detectors 6, 7, 8 are the well-known Geiger-Mueller type gammaparticle counters.

It is noted that various arrangements of the source and detectors can bemade with respect to each other, the vessel wall, and the liquid level.For examples, the detectors could be horizontally extended, or could besituated immediately adjacent the shell wall. The technique of variablegamma ray stimulation of the G-M counters proportional to varying level15 positions--all within the art of level detection with radiationdevices-is described in the special instance of a thick-walled vesselwith thin-walled source and detector containers inside the vessel butpreserved from its contents.

In combination with a radiation-type measurement and control device, thepreferred mode depicted in the drawings incorporates the invention asdisclosed below.

The Source:

FIG. 2 illustrates the radiation source assembly 5. It consists of aradioactive material 5 a and suitable shielding 5 b, a spacing andsupport rod 17, a weighted collar structure 18, and handle 19. In thisembodiment, structure 18 is strictly to limit the travel of source 5 ain its container 3, i.e., the collar is not threaded and is without lugsor seats or O-rings to lock or seal with the container 3 opening. Theweight of the source unit holds the unit in place in its container, thusproviding the maximum in simplicity and ease of emplacement and removal.Of course, if it were desired, a lock arrangement could easily beprovided between head 18 and the opening of container 3 with, forexample, a connector such as disclosed in my US Pat. No. 3,545,490.

The Protection of the Source:

Since the vessel of FIG. 1 is shown at a subsurface location in the sea,and since the collar to container connection does not of itself isolateor protect the source assembly 5 or the internal of container 3, it isnecessary to provide this protection from destructive marine life andchemical action in another manner. Thus, the container 3 is filled witha material to occupy the annulus 20 between 5 and 3. This material isheavier than water, insoluble in water, non-corrosive, and inimical tomarine life. Many such materials of liquid or plastic state exist, e.g.,various silicone liquids and petroleum greases. After filling container3, assembly 5 is merely lowered into place into container 3. Sourceassembly 5 may be removed and reinserted without adding new material tothe container 3 each time, as reinsertion of'unit 5 will merely displacethe amount of water allowed to enter when unit 5 was withdrawn.

The Detectors:

The housing 21 for network 16 is designed to join the container 4 upperopening 22 in the same manner as disclosed in the second paragraph abovefor the collar 18 container 3 union. Added support is provided by leg23. Leg 23 is also adjustable in length to vary the location ofdetectors 6, 7, 8 and thus the height of fluid level 15 desired to beheld within vessel 1.

FIG. 3 illustrates the detector elements assembly 24. It con sists of acase 25 for the G-M counters. There may be one or more counters arrangedwithin the case 25, depending on the number of signalling and controlfunctions desired. FIG. 1 shows a set of three detectors to controlhigh, low, and normal level. Any one or two of these functions may bepresent alone, depending on design specifications. Cooling vanes orports 26 are shown for dissipation of the heat of the power sourcewithin electronic network 16. The network 16 is known in the art oflevel control by radioactive means and so is not disclosed. A suitablehandle 27 is provided. Lead wires 28, 29, 30 of network 16 exit housing21 for control of input valve 12, for surface manifestation and overridecontrols, and for control of output valve 14, respectively. Theconnector clips 3] permit underwater wiring connections without wettingor fouling the terminals of the leads, and can be of the type suppliedby Electro Oceanics, Compton, California.

The Protection of the Detector:

A prime requirement of the operating environment for a radioactive levelcontrol system is that detector elements of the Geiger-Mueller type beoperated below the temperatures expected in the vessel 1. Although gammaray emission is independent of temperature, the detectors exhibit theso-called avalanche effect in current discharge when their temperatureis excessive. Temperatures in the vessel may be expected to be commonly-220 F. A heat exchange between the detectors and the atmosphere (seawater) is provided by flow of the cooler water through container 4.Openings 32, 33 are provided for entrance and exit of the water, and theconduit 34 carries this flow through container 4. Conduit 34 is formedas the container 4 wall/case 25 annulus. F low through conduit 34 is aconvection current generated by the temperature difference between theheated container wall and the cooler sea. A centralizer 35 is fixed tocase 25 to insure conduit 34 remains effectively open should leg 23 beextended (as to adjust the detectors position) so that housing 21 didnot rest upon the opening 22 of the container 4.

Prevention of marine growth and deleterious chemical action on thecontainer 4/case 25 structure is necessary. The heat present in vessel 1should prevent damage from marine life, and a suitable coating orcorrosion-proof metal will be used in the container 4 and case 25 tominimize corrosive chemical action.

Conclusion It is seen that the preferred embodiment of the inventionwill provide a reliable level detection, manifestation, and controlmeans for subsea oil field process vessels. This embodiment thereforecombines a means without moving parts and free from the manydifficulties of mechanical systems in a system wherein numerousadvantageous and novel features reside, to wit:

1. a radiation-type level control system may be employed;

2. the emplacement and removal of the source and detector assembliesfrom the vessel is highly simplified;

3. the vessel is not opened to service or replace the level controls,and the source and detector assemblies can be handled separately;

4. the level controls and their containers are well protected from theharmful subsea environment;

5. the wall thickness of the vessel is not penetrated by the radiationof the source assembly, thus minimizing the radioactive mass employed inthe level control system;

6. cooling of the detector assembly is provided by natural convectioncurrents in the ambient environment, and without installation of pumpsor power sources;

7. automatic high and low shutdown controls are provided which do notrequire continuous surface monitoring;

8. a unitary electronics network and power source can besurface-calibrated and installed at the subsea location;

9. the electronics network and detector elements assembly can bepressure tested as one unit at the surface;

l0. the positions of the levels desired can be adjusted underwater; and

ll. present submarine vehicles can easily accomplish all emplacement andremoval tasks.

It is emphasized that this level control system can be employed in anysubsea vessel in which it is desired to observe and/or control theliquid levels, provided the gamma ray emission from the source matterdoes not itself contaminate the vessel contents.

This system could well be employed on surface vessels, with the coolingof the detector elements accomplished by either the air of theatmosphere, or by a heat exchange medium circulated about the detectorassembly through the container openings by suitable pump means.

In addition, other configurations of the source-detector arrangementcould certainly be made within the scope of this invention. It isimportant only that the detectors respond in some direct way to theemissions from the source to control the fluid level.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the method and apparatus.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theinvention.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterset forth above or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. A level detector system for a vessel containing fluid, in-

cluding,

a first container arranged to extend through a section of the vesselwall and having its interior accessible from the exterior of the vessel,

a source of radiation mounted within the first container,

a second container arranged to extend through a section of the vesselwalls so that its external surface intersects the level of fluid withinthe vessel and its interior is accessible from exterior of the vessel,

a detector of the radiation of the source mounted within the secondcontainer at a position where the radiation will be at least partiallyshielded by the fluid within the vessel at a predetermined level of thefluid in the vessel so that the detector responds to the radiation ofthe source to indicate the level of the fluid in the vessel,

and the second container arranged so that its interior is exposed ateach end to the ambient fluids of the environment which is external tothe system to cause convection currents of said fluids through thelength of the second container for cooling the radiation detector.

2. The system of claim 1 in which,

the detector of the radiation mounted within the second containerconsists of a plurality of detectors spaced in linear relation to oneanother and at a predetermined distance one from another, and in whichcircuits responsive to the electrical energy generated by the detectorsin response to the radiation received are provided to indicate thechange of the level of fluids in the vessel.

3. The system of claim 1 including, a selected protective materialwithin the first container and UNETED STATES PATENT OFFICE wrmmm er@EQ'HN Patent No. 3?65L"q58 Dated April 97 In ent0r(5) S BuII'uS @t a].

' It is certified that error appears in the above-identified patent andthat said Letters Patent 'are hereby corrected as shown below:

' Column 1, line 54, "produce should readproduct column 3, line 62,"3,545H490" should read 3, 58,218

Signed andsealed this 19th day ofDecenfloer' 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GO TSCHALK Attesting Officer Commissionerof Patents DRM PC4050 (10459) uscoMM-Dc 6O376-P69 U. 5. GOVERNMENTPRINTING OFFICE: 1969 0-365-334.

1. A level detector system for a vessel containing fluid, including, afirst container arranged to extend through a section of the vessel walland having its interior accessible from the exterior of the vessel, asource of radiation mounted within the first container, a secondcontainer arranged to extend through a section of the vessel walls sothat its external surface intersects the level of fluid within thevessel and its interior is accessible from exterior of the vessel, adetecTor of the radiation of the source mounted within the secondcontainer at a position where the radiation will be at least partiallyshielded by the fluid within the vessel at a predetermined level of thefluid in the vessel so that the detector responds to the radiation ofthe source to indicate the level of the fluid in the vessel, and thesecond container arranged so that its interior is exposed at each end tothe ambient fluids of the environment which is external to the system tocause convection currents of said fluids through the length of thesecond container for cooling the radiation detector.
 2. The system ofclaim 1 in which, the detector of the radiation mounted within thesecond container consists of a plurality of detectors spaced in linearrelation to one another and at a predetermined distance one fromanother, and in which circuits responsive to the electrical energygenerated by the detectors in response to the radiation received areprovided to indicate the change of the level of fluids in the vessel. 3.The system of claim 1 including, a selected protective material withinthe first container and disposed about the radiation source assembly asprotection from the deleterious effects thereupon of the ambient fluidsof the environment which is external to the system.